Abstract:  The quality was studied on the viable cells number,quick solution and fermentation in contrast with the freeze drying and vacuum drying yoghurt powder. The results showed that the quality of the two types of yoghurt powder was of great difference. Compared with the vacuum drying, the viable cells number, quick solubility and fermentability of the freeze drying yoghurt powder was better, while the viable cells number were 73.11% and 38.45%, the fermentative activity were 85°T and 78°T, the solidify time were 3.5h and 5.5h respectively. The yoghurt powder had better quality when it was mixed with 45℃ water in a ratio of 1:4～5. The optimum content of water for the freeze drying yoghurt powder was 1.5%～3.0%.

Key words: freeze drying, vacuum drying, yoghurt powder, quality, contrast study